This invention relates generally to the field of venting devices, and in particular, to passive venting devices.
Virtually all buildings and enclosures where human activity takes place require venting of one type or another. The type of venting device employed will depend on the kind of enclosure to be vented. For example, bathrooms containing showers typically have active vents with fans to vent steam to the outdoors. Kitchens, particularly in restaurants and hotels, similarly have powered vents for removing smoke and steam to the outdoors.
Other types of enclosures, such as attics, do not require active venting. However, such enclosures do typically require a passive vent to allow for air flow from the enclosure to the atmosphere. Such venting is required, for example, to prevent a buildup of moisture in the enclosure. Notably, the venting of attic spaces by this method is required by the building codes of many jurisdictions.
Passive vents do not include a mechanism for forcing air out of the enclosure. Rather, they simply include a vent structure in the form of an air conduit which allows air flow. Passive vents are well-known and have been extensively used in the past. Although often formed of metal, good results have been achieved more recently with plastic vents.
House attics and other similar enclosures are sometimes vented simply by one or more passive venting devices on the roof. The passive venting devices are each positioned above a ventilation passage in the roof which permits air to flow from the enclosure to the outside.
In other cases, a more sophisticated venting system is used. Such a system includes intakes for bringing air into the enclosure, operating together with vents permitting air to flow out of the enclosure. Ideally, such a system causes outside air to flow through the enclosure. In this way, gases and vapours in the enclosure, including water vapour, are carried out of the enclosure by the air flow through the vents. Moisture and temperature are thus equalized between the enclosure and the outside.
For example, on sloped roofs, it is common to have intakes installed at the eaves for bringing air into the attic. Vents for venting air out of the attic are installed higher up on the roof, near the peak. Thus, warm moist air within the enclosure rises and flows out through the vents. Air from the outside is taken into the enclosure through the intakes because of the pressure differential created by the outflow of air through the vents.
Historically, part of the function of a vent has been to allow the flow of air through the passage, without permitting moisture, such as rain or snow, to enter the enclosure through the passage. Thus, prior art vents have included features preventing the same.
For example, U.S. Pat. No. 6,155,008 issued Dec. 5, 2000 to McKee (hereinafter xe2x80x9cMcKeexe2x80x9d) discloses a passive venting device for venting a building enclosure. The device includes a base member having a vent structure therein. The vent structure is to be positioned over the ventilation passage which extends through the roof of the enclosure. The device also includes a cap member which is positioned over the vent structure to prevent rain and snow from falling directly into the vent structure and through the passage. The cap member, however, is spaced apart from the base to allow air to flow between the cap and the base and through the vent structure.
It has been found that, despite the presence of a cap over the vent structure in devices such as the McKee device, precipitation, such as snow, can occasionally pass into the enclosure through the vent structure. This is because, with the McKee device, snow accumulates at the base of the device, near the bottom edge of the cap. Experience has shown that wind travelling along the sloped roof will often drive the snow up under the cap and through the vent structure into the attic.
This problem can be exacerbated in cases where the eaves intakes become blocked, are improperly installed, or do not exist. In such cases, the vent can act as an intake vent. For example, where there is no air inflow from the eaves, when air flows out of one vent, it must flow in through another vent. Or, air may flow out through one region of the vent structure of a vent while flowing in through another region the vent structure. In either event, if any air flows into the vent, snow or rain present near the vent can be drawn into the enclosure. Any snow blown toward the vent structure will be more likely to enter if the air flow passes into the vent.
It has also been found that, though devices such as the McKee device are generally effective in blocking the entry of rain into the attic, they can leak during extreme weather conditions such as torrential rain. There are at least two reasons for this. First, torrential rains are often accompanied by high winds, which can drive rain drops into the vent structure in the same way described above with respect to snow. Second, because there is a great deal of rain falling very hard, rain drops can strike the device, bounce up under the cap, and enter the vent structure. As with snow, more rain will enter the attic in cases where the device is acting as a full or partial intake.
Another issue with respect to roof vents is their use in conjunction with roofing materials such as shingles, shakes or tiles. The venting device disclosed in McKee includes a wide nailing flange which is nailed to the roof to permit shingles to be lapped over the flange. Thus, on a sloped shingled roof, shingles are installed on top of the flange on the top end and side ends of the flange. At the bottom, the flange overlaps the shingles. In this manner water is shed off the roof.
To provide an appropriate seal for the roof, shingles are typically lapped over the flange right up to the vent structure in the centre of the device. One reason that this is done is to reduce the probability that water will enter under the sides of the shingles. However, two problems arise with this approach.
First, the vent structure often has an uneven shape, which makes it difficult or inconvenient to install shingles right up against the vent structure. Doing so would require the shingles to be cut in the same uneven or jagged pattern as the vent structure. Thus, there is often space between the vent contours of the structure and the shingles, permitting water to work its way under the shingles from the side.
Second, the shingles are installed on top of the flange, where they can interfere with the air flow of the vent. This is because, in devices such as that disclosed in McKee, air flows through a gap formed between the cap and the flange. On the one hand, the gap is located as low as possible to reduce the likelihood of water getting into the vent structure. On the other hand, a low gap means that the shingles, if placed over the flange and in the gap, will reduce the height of the gap and hence the air flow.
Because shingles, in particular, are relatively thin, this second problem may not be particularly severe when shingles are used. However, other commonly used roofing materials, such as, for example, cedar shakes or clay tiles, are significantly thicker. Thus, shakes and tiles often cannot be used with prior art devices such as McKee, as their thickness interferes with the air flow through the gap and thus into the vent.
Therefore, what is desired is a passive venting device that is simple and inexpensive to manufacture and install. The device will allow for the efficient passive venting of an enclosure while preferably eliminating or substantially reducing the entry of precipitation into the enclosure through the device. The device will also preferably be usable with a variety of roofing materials, including shakes and tiles, without air flow through the vent being interfered with.
Therefore, according to one aspect of the invention, there is provided a passive venting device for venting a building enclosure to an outside, the device comprising:
a base member, including an attachment portion for securing the base member in fluid communication with a ventilation passage through a surface of the building enclosure, and a vent structure for permitting gas and vapour to pass through the device, the vent structure having a vent opening;
a cover member mounted to the base member, the cover member and the base member being sized, shaped and positioned so as to permit the flow of gas and vapour from the vent opening to the outside;
a precipitation baffle, extending from at least one of the base member and the cover member, the precipitation baffle being sized, shaped and positioned both to interfere with the entry of precipitation from the outside into the enclosure through the vent opening, and to permit gas and vapour to flow to the outside through the vent opening.
According to another aspect of the invention, there is provided a passive venting device for venting a building enclosure to an outside, the device comprising:
a base member, including an attachment portion for securing the base member in fluid communication with a ventilation passage through a surface of the building enclosure, and a vent structure for permitting gas and vapour to pass through the device, the vent structure having a vent opening;
a cover member mounted to the base member, the cover member having a ventilation pathway extending therethrough, the ventilation pathway being sized, shaped and positioned to permit the flow of gas and vapour from the vent opening to the outside along the ventilation pathway;
the cover member being sized, shaped and positioned on the base member such that roofing material may be installed in abutment with the cover member, the ventilation pathway having an exit from the cover member, the exit being spaced from the base member so as to permit the roofing material to be installed abutting the cover member without interference with the exit.